The present application claims priority to Japanese Application No. P2000-162114 filed May 31, 2000, which application is incorporated herein by reference to the extent permitted by law.
The present invention relates to a method of manufacturing a semiconductor device including the step of activating an impurity doped to a semiconductor layer by an energy beam. Specifically, the present invention relates to a method of manufacturing a semiconductor device preferably used for manufacturing a top-gate thin film transistor (TFT) on a low-heat-resistant substrate.
In recent years, polycrystalline silicon (Si) TFTs formed on glass substrates are used for picture elements and drivers of liquid crystal displays as switching function devices, and also have been developed as semiconductor memories. In the semiconductor devices such as TFT and the like, it is necessary that the substrates are light, shock-resistant, and have a flexibility so that they are not damaged when stress is being applied to some extent. Therefore, glass substrates, silicon substrates or the like have been used as the substrates in the related art. The glass substrates have low heat resistance (heat-resistant temperature is 400xc2x0 C.). Therefore, heat treatments on semiconductor layers and the like have been performed by maintaining the substrate temperature relatively low through performing local heating using energy beams such as lasers, infrared lamps and the like.
Recently, plastic substrates have come into use since the plastic substrates are lighter and more shock-resistant compared to the above-mentioned substrates. However, the plastic substrates made of polyethylene terephthalate (PET) or the like have the heat-resistant temperature of about 200xc2x0 C. or below, which is lower than that of glass substrates.
Therefore, it is necessary to manufacture a semiconductor device using the plastic substrate by performing all the manufacturing steps at 200xc2x0 C. or below. Specifically, not only a heat treatment performed for crystallization or activation of an impurity, but also a fabrication of thin films such as silicon dioxide (SiO2) films used for gate insulating films, interlayer insulating films and the like is performed under the temperature condition at 200xc2x0 C. or below, which is generally performed at a temperature higher than 200xc2x0 C.
However, in general, it is impossible to activate the impurity doped into the semiconductor layer at 200xc2x0 C. or below. Also, if SiO2 films are formed at 200xc2x0 C. or below, there are a large amount of defects in the obtained SiO2 films and in the interface between the obtained SiO2 films and the semiconductor layer. A method of removing the defects by applying a heat treatment after forming the SiO2 films is not applicable to the plastic substrates since the method needs to be performed under the condition at least at 400xc2x0 C. or more.
Also, even if the above-mentioned heat treatment is performed by locally heating the surface of the device by an energy beam, temperatures in the insulating layer and the layers thereunder raises suddenly since the energy beam instantly performs high-temperature heating. As a result, the plastic substrates, which have very low thermal resistance, are sometimes damaged by the heat of the irradiated beam.
The invention has been designed to overcome the foregoing problems. The object of the invention is to provide a method of manufacturing a semiconductor device, which can manufacture a semiconductor device having an excellent characteristic on a low-heat-resistant substrate.
A method of manufacturing a semiconductor device of the invention comprises the steps of: forming a semiconductor layer on a substrate; selectively forming a metal layer on the semiconductor layer with an insulating layer inbetween; selectively doping an impurity into the semiconductor layer using the metal layer as a mask; forming an energy absorption layer so as to cover the insulating layer and the metal layer; and activating the impurity doped into the semiconductor layer by irradiating an energy beam from the energy absorption layer side.
In the method of manufacturing a semiconductor device of the invention, the irradiated energy beam is once absorbed in an energy absorption layer, and through the energy absorption layer, indirectly heat a metal layer, an insulating layer and a semiconductor layer thereunder without damaging the low-heat-resistant substrate made of plastic or the like. Thereby, an impurity in the semiconductor layer is activated and defects in the insulating layers are removed.
Other and further objects, features and advantages of the invention will appear more fully from the following description.